1. Field of the Invention
The present invention relates to a touch panel mainly used to operate a wide variety of electronic equipment and a manufacturing method thereof.
2. Background Art
In recent years, a wide variety of electronic equipment such as mobile phones and car navigation systems has advanced in functions and become diversified. Along with this, equipment like following is increasing in number. That is, to select respective functions of the equipment, a user operates to press down a touch panel by a finger, a pen or the like while viewing a display element such as a liquid crystal display (LCD) device through a light transparent touch panel. The touch panel is attached on the front surface of the display element. Such equipment requires having a highly visible touch panel with reliable operability.
A conventional touch panel of this kind is described with reference to FIG. 3. FIG. 3 shows a cross-sectional view of a conventional touch panel. The drawing is shown on an expanded scale in a thickness direction so that the configuration can be understood easily. The touch panel includes light transparent top substrate 51 and bottom substrate 52. Light transparent top conductive layer 53 made of indium tin oxide or the like is formed on the bottom surface of top substrate 51, and bottom conductive layer 54 is formed similarly on the top surface of bottom substrate 52.
Dot spacers (not shown) made of insulating resin are formed on the top surface of bottom conductive layer 54 with a prescribed distance therebetween. A pair of top electrodes (not shown) are formed on both ends of top conductive layer 53, and a pair of bottom electrodes (not shown) are formed on both ends of bottom conductive layer 54 perpendicularly to the top electrodes.
Frame-like spacer 55 is disposed on the periphery of top substrate 51 and bottom substrate 52 therebetween. Top substrate 51 and bottom substrate 52 are bonded together on their peripheries using adhesive layers (not shown) coated on either or both top and bottom surfaces of spacer 55. The touch panel is thus formed with top conductive layer 53 and bottom conductive layer 54 facing each other with a prescribed clearance.
The touch panel thus formed is disposed on the front surface of a display device such as LCD and is mounted under window frame 57A in housing 57 of electronic equipment. Pairs of the top and bottom electrodes are then connected to electronic circuits (not shown) of the electronic equipment via a wiring board or the like.
In the above configuration, when a user operates to press down a place in the top surface of top substrate 51 by a finger, a pen or the like in response to the indication at the back of the touch panel, top substrate 51 bends down, causing top conductive layer 53 to contact with bottom conductive layer 54 at the pressed place. The electronic circuit then applies voltages to the top electrodes and to the bottom electrodes sequentially. The electronic circuit detects the pressed place by a ratio of the voltage between the top electrodes and the voltage between the bottom electrodes, thereby performing to select a wide variety of functions of the electronic equipment.
At this time, any problem will not occur particularly when the user operates to press down in the center of the top surface of top substrate 51 as indicated by arrow C. In some cases, however, intending to operate to press down near the right or left end of the top surface of top substrate 51, a user may mistakenly press down the top surface of housing 57 as indicated by arrow D, for instance. When a large force is applied on window frame 57A, an end of window frame 57A deforms downward allowing the end of top substrate 51 to bend down, causing top conductive layer 53 to contact with bottom conductive layer 54 near the inner periphery of spacer 55.
In another case, when a relatively large foreign matter such as a dust happens to adhere between an end of the top surface of top substrate 51 and the bottom surface of window frame 57A, the foreign matter will press to bend top substrate 51 downward. Therefore, the end of top conductive layer 53 contacts with bottom conductive layer 54 eventually. Even in the case that the end of top conductive layer 53 contacts with bottom conductive layer due to the reasons described above, the electronic circuit would detect erroneously as if the touch panel is operated to press down, causing an operation error in the electronic equipment.